Mailtotoaddrquery

Mailtotoaddrquery is a term used in discussions of email infrastructure to describe a conceptual pattern in which a mailto URI is employed to perform an address-related query. It is not an official protocol or standard; there is no widely adopted RFC for mailto:addrquery. In this concept, a client constructs a mailto URI that encodes a lookup request for a recipient address, rather than just initiating a message.

In a typical workflow, a user agent or server extracts the query portion from the URI and forwards it to a directory or mailbox service. The service then resolves the input to metadata such as a canonical address, aliases, trust status, or mailbox properties, and returns the result through a supported channel (for example, an HTTP API, LDAP, or a disambiguation page). The mailto scheme itself is primarily designed to open a new message window, so using it for queries requires additional intervening services or conventions.

Potential use cases include automatic contact provisioning, lightweight address verification before sending mail, deduplication in unified address books, and routing decisions in mail systems that support dynamic address resolution. It is more likely to appear in prototypes, enterprise toolchains, or documentation examples rather than in public mail protocols.

Security and privacy concerns are central. Exposing directory data via mailto queries can reveal sensitive information, so access control, encryption, and auditing are important. Input validation is necessary to prevent injection or abuse, and operators should prefer dedicated directory queries over generic URI-based lookups for production deployments.

Related concepts include the mailto URI scheme defined in RFC 6068, LDAP or Active Directory as sources of address data, and general address verification techniques such as SMTP MAIL FROM validation, DNS-based MX checks, and list hygiene practices.